The present invention relates to a device for examining the degree of filling of a zone of a cigarette.
in a disclosed device, light is radiated end-on from a certain spacing onto the cigarette end and reflected by the tobacco fibres into a light receiver which is likewise arranged end-on. The greater the reflected light, the better is the degree of filling. Reject cigarettes are therefore those in which the received light falls below a predetermined threshold value. An example of such a device is disclosed in U.K. Pat. No. 1,347,221 in which a measuring probe comprises light conducting fibres. It is an advantage of such a device that it only requires space end-on so that one can simultaneously examine several cigarettes, for example a cigarette block to be packaged, with a corresponding plurality of devices of the same type. Unfortunately, the distinction between a good and a reject cigarette is however fairly inaccurate, since on the one hand in the case of badly filled cigarette end, light reflected by fibres disposed more deeply can reach the receiver and thus falsify the measurement and, on the other hand, light is reflected past the receiver in the case of well filled cigarette ends.
The fact that slight changes of the spacing between probe and cigarette end falsify the measurement shows how small the capability of resolution is, so that complicated devices have been created for compensation of fluctuations in spacing. In this respect reference is made to DE-OS No. 26 25 001.
An improved capability of resolution can be obtained by determining the light permeability of the cigarette end. According to FIG. 5 of DE-OS No. 26 53 298, a light exit surface and light entry surface are arranged laterally and end-on, respectively, with respect to the cigarette and the better the degree of filling, the less light reaches the light receiver. In the case of this disclosure, the cigarettes must however be accessible laterally as well as end-on so that only individual examinations are possible.